Stabilization of styrene



Patented Sept. tees 2,215,255

Unitas STATE-S PATENT QFFHCE.

2,215,255 STABIIJZATION or STYRENE Sylvia M. Stoesser and Ray H. Boundy,Midland,

Mich, assignors to The Dow Chemical Company, Midland, Mich a corporationof Michigan .No Drawing. Application June 28, 1938, l i Serial No.216,297

scams. (Cl. 23-450) This invention concerns a method for the stasure ina vessel equipped with a reflux'conbilization of styrene againstpolymerization and denser to prevent loss of. styrene through vaporalsoconcerns the stabilized compositions so preization. Since thehydrocarbon gases employed pared. vas stabilizing agents are onlysparingly soluble It is well-known thatstyrene polymerizes quite instyrene, they may thus be removed in a very 5 rapidly upon standing atroom temperature and short time. If desired, the gases may be colevenmore rapidly when warmed or exposed to lected and stored for re-use.)The styrene is in light. For example, monomeric styrene, which no waychanged by the stabilization treatment is a thin mobile liquid,polymerizes to a thick and, after removal'of the stabilizing agent, maygummy mass during storage for four months in be polymerized to producepolymers which are m the darkroom temperature. An equal amount identicalwithpolymers prepared from unstaof polymerization occurs when monomericstybilized material. rene is exposed to ordinary daylight at room tem- 7Although some degree of stabilization is seperature for only threeweeks. Longer storage cured by the presence of mere traces of the newunder either of these conditions results in further stabilizing agents,we prefer to prepare our sta- 13 polymerization with the eventualformation of bilized styrene composition by passing the dea toughresinous solid which is inconvenient to' sired gas into liquid monomericstyrene until the handle as well as unsuitable for many of the useslatter has been saturated with the gas. Smaller to which styrene isordinarily put. amounts of the stabilizing agent may of course Becauseof this tendency toward polymerizabe employed in many instances, thesmallest 20 tion, storage and shipment of monomeric styrene practicalamount beingdependent upon the parhas been a diflicult problem. We areaware that ticular hydrocarbon gas employed as the stabia number-ofsubstances, e. g., quinone, trinitrollzing agent, the period over whichthe matebenzene, etc., have been proposed as inhibitors rial is to bestored without undergoing apprefor the polymeri ation of S y e, but ySuch clable polymerization, the temperatures encoun- 25 subs an s ar xpesive. do not v e vtered during storage, etc. If desired, styrene P op yof b t n Po ymerization to a suimay be saturated at superatmosphericpressure flcient degree, or cannot readily be removed from with thegaseous stabilizing agent in order to the Stabil e composition torecover the styrene obtain a higher concentration of the latter in inSubst y P and polymerizable condithe styrene than is possible atatmospheric pres- 30 tion. e sure, but such use of elevated pressure isincon- An object of this invention is,to provide cervenient and usuallyunnecessary. tain new a ents f th stabilization of styrene The followingtable presents data illustrating which may readily be removed to recoverthe the degree of stabilization secured by employing styrene insubstantially pure, colorless and readthe gases propane, propylene,isobutane, and 1011- 85 ily polymerized form. Another object is toprotylene as stabilizing agents. In each experiment, vide stabilizingagents which are efiective in small a, saturated solution of the gas instyrene was concentrations, inexpensive, and convenient to stored atroom temperature for the time and handle other objects will be apparentfrom the under the conditions stated in the table. The 40 followingdescription of the inventive symbols 11-], used to indicate thecondition of the M We have found that i low molecular material after thestated time,,carry the following weight hydrocarbon gases, namely,propane, promeanings: pylene, isobutane, and butylene, possess theproperty of inhibiting the polymerization of styrene, and that styrenecontaining one or more of these gases in solution may be held under theusual conditions of storage and shipment over long periods of timewithout undergoing appreciable polymerization. When desired, the liquido0 styrene may be recovered from such stabilized (d) The material isveryflscous j m compositions in a substantially pure, colorless, (6) Thematerial i a Very d readily polymerized form by vaporizing on (f) Thematerial is a tough solid resm.

the dissolved gas. Removal of the gases in this A symbol followed byindicates that the manner is usually carried out by boiling thestamaterial was polymerized to a somewhat lesser 5 bilized styrene underordinary or reduced presextent than that designated by the symbolitself,

(a) No thickening or other visible change occurred;

(b) The material is slightly more viscous than freshly distilledstyrene;

(c) The'material is a viscous but free-flowing i. e., a rating of b+,for example, indicates that the condition of the material wasintermediate between that designated by "b and a.

tion' sufiicient to inhibit polymerization of the styrene.

2. A composition of matter comprising styrene Other modes oi applyingthe principle oi our invention may be employed instead of thoseexplained, provided the ingredients stated by any of the followingclaims or, the equivalent of such stated ingredients be employed.

We therefore particularly point out and distinctly claim as ourinvention;

1. A composition of matter comprising styrene having dissolved therein ahydrocarbon gas selected from the group consisting oi propane,propylene, isobutane, and, butylene, in a proporhaving isobutanedissolved therein in a proportion suificient to inhibit polymerizationof the styrene. 3. A composition of matter comprising styrene havingbutylene dissolved therein in a proportion sumcient to inhibitpolymerization of the styrene. 4. A composition of mattercomprisingstyrene having propylene dissolved therein in a proportion suiiicient toinhibit polymerization of the styrene.

SYLVIA M. STOESSER. RAY H. BOUNDY.

